In order to improve the transmission efficiency of the wireless communication system, MIMO has become an inevitable choice for the wireless communication at present and in the future. In the MIMO-OFDM system, the usage of multiple transmitting/receiving antennas greatly increases the number of unknown parameters in the system. These unknown parameters shall be estimated using known pilot or training signals, but extra pilot sequences occupy a lot of physical resources, and the usage of multiple antennas brings a great challenge to the estimation of the unknown parameters.
For the convenience of allocating the physical resources in a high efficiency, a physical frame is usually divided into a plurality of sub-frames in the time domain, and each sub-frame is divided into a plurality of basic allocation units, i.e., resource blocks (RBs), in the frequency domain. For example, in the latest LTE standard, a frame of 10 ms includes 10 sub-frames, and each sub-frame includes 14 OFDM symbols; each sub-frame is divided into sub-blocks in the unit of 12 sub-carriers in the frequency domain, and the time-frequency RBs of the 12 sub-carriers and 14 OFDM symbols constitute a basic RB. FIG. 1 is a schematic diagram of a pilot distribution in a physical resource unit (time-frequency two-dimensional) when there are 4 transmitting antennas.
The design schemes of the reference signal of the conventional multi-transmitting antenna system are mainly based on the orthogonal pilot design criterion, i.e., resources occupied by the pilots of respective transmitting antennas are orthogonal to each other, so as not to cause mutual interferences between the receiving ends. In the LTE Rel-8 standard, the highest configuration of supportable transmitting and receiving antennas is 4×4. In order to support higher data transmission rates and more effectively utilize the valuable spectrum resources, an antenna configuration up to eight-transmitting and eight-receiving antenna shall be adopted in the currently discussed LTE Release-10 (LTE-A). In that case, if the orthogonal RS design is still used, the reference signal will occupy a lot of physical resources, which severely challenges a high-efficient and reasonable design of the reference signal. For this reason and in consideration of the pilot design of the LTE and LTE-A hybrid system, a design that uses special pilot and common pilot may be taken into account. The common pilot is adopted for the channel quality of the user measurement system of the LTE-A, and the pre-coded matrix or the like is used. The common pilot of Antennas 0 to 3 in the eight transmitting antennas of the LTE-A base station and the common pilot of the four transmitting antennas defined in the LTE have the same pilot pattern, i.e., a pilot pattern as illustrated in FIG. 1. The common pilot of Antennas 4 to 7 needs to occupy other time-frequency resources for a transmission. The special pilot is only available for an LTE-A user to whom a certain RB is scheduled, so as to perform a channel estimation and demodulate the data.
At present, some people propose to distinguish the sub-frames in each 10 ms frame in a time division multiplexing manner. That is, to classify the sub-frames into three categories: the first category is the LTE sub-frame, in which all RBs are scheduled to the LTE user; the second category is the LTE-A sub-frame, in which all RBs are scheduled to the LTE-A user; and the third category is the blended sub-frame, in which all RBs may be scheduled to the LTE user or the LTE-A user. In addition, some people propose to transmit the LTE-A common pilot in the LTE sub-frame. In the prior art, on one hand, the LTE-A common pilot interferes the data transmitted by the RBs in the LTE sub-frame; on the other hand, since some sub-frames can only be scheduled to the LTE-A user or the LTE-A user, the flexibility of system scheduling is decreased.
To be noted, the above descriptions of the conventional art are only made for the convenience of clearly and completely describing the technical solutions of the present invention, and for the convenience of the understanding by a person skilled in the art. It shall not be deemed that the above technical solutions are well known to a person skilled in the art just because these technical solutions have been described in the Background section of the present invention.
The literatures of the present invention are listed as follows and incorporated into this Specification by reference as if fully set forth herein.    1. [Patent Literature 1]: Han Jin-Kyu, et al., Method and apparatus for managing control channel in a mobile communication system using multiple antennas (US 20080212550 A1);    2. [Patent Literature 2]: Yoshii Isamu, et al., Radio Transmitter and pilot signal inserting method (US 20080107158 A1);    3. [Patent Literature 3]: Song Young-joon, et al., Pilot signals for synchronization and/or channel estimation (US 20080298438 A1);    4. [Patent Literature 4]: Budianu Petru Cristian, et., al. Methods and apparatus for improved estimation of selective channels in an OFDMA system with dedicated pilot tones (US 20080232484 A1);    5. [Patent Literature 5]: Malladi Durga Prasad, et al., Hybrid pilot configuration (US 20080225993 A1);    6. [Non-patent Literature 1]: R1-090706, “DL Reference Signal Design for 8×8 MIMO in LTE-Advanced”, Fujitsu, 3GPP RAN1 #56 meeting, Athens Greece;    7. [Non-patent Literature 2]: R1-090619, “DL RS Designs for Higher Order MIMO”, Samsung, 3GPP RAN1 #56 meeting, Athens Greece.